The present invention relates to a method for the preparation of a polyarylene sulfide or, more particularly, to a method for the preparation of a polyphenylene sulfide having an outstandingly small content of salt in a process by which the polymer product can readily be separated from the reaction mixture.
Polyarylene sulfide or, typically, polyphenylene sulfide, which is referred to as PPS hereinbelow, is a partially heat-curable thermoplastic resin having excellent characteristic properties as a so-called engineering plastic in respect of the remarkable resistance against various chemicals, good mechanical properties retained over a wide range of temperature, heat-resistant rigidity and others.
PPS is usually prepared, as is described in Japanese Patent Publication No.52-12240, by the reaction of 1,4-dichlorobenzene and sodium sulfide in an organic amide as the solvent in the presence of a metal carboxylate as the catalyst. This method is, however, disadvantageous due to the high production cost of the PPS because the amount of the relatively expensive metal carboxylate required for sufficiently accelerating the reaction is very large in the range, for example, from 0.7 to 4 moles per mole of the sodium sulfide. Moreover, the PPS product unavoidably contains as much as 1000 to 3000 ppm of sodium chloride as an impurity produced by the reaction as a byproduct. Such a high content of the sodium chloride impurity is of course detrimental in the PPS polymer, especially, when the polymer is used in applications in the fields of electric and electronic technologies due to the possible decrease in the insulation of the circuit in a humid condition to cause errors in the operation of the circuit. Therefore, such a PPS polymer of high impurity content must be purified again before it is used.